1. Field of the Invention
The present invention relates to a position detecting switch for detecting the position of an operating member selecting a range among a plurality of ranges and, more particularly, to a position detecting switch that detects the operating member position by a movable contact point, movable cooperatively with range shift operation of an operating member, contacting a stationary contact point corresponding to the selected range.
2. Description of the Related Art
In a motor vehicle, a driver operates a shift lever to select one of six or seven ranges of an automatic transmission to control vehicle running conditions. These ranges typically include a parking range (hereinafter, referred to also as "P range"), a reverse range (hereinafter, referred to as "R range"), a neutral range (hereinafter, referred to as "N range"), a drive range (hereinafter, referred to as "D range"), a second speed range (hereinafter, referred to also as "2nd range"), and a first speed range (hereinafter, referred to as "L range"). A position detecting switch is provided for detecting the shift lever range position selected by the driver to control the automotive automatic transmission. Such a position detecting switch is normally mounted directly on the automatic transmission (hereinafter, referred to also as "AT").
The position detecting switch has a plurality of range positions corresponding to the ranges of the automatic transmission. When a driver selects a transmission range, the position detecting switch detects the range position and outputs a position detecting signal. Based on the position detection signal from the position detecting switch, an electronic control device formed by, for example, a microcomputer, controls the automatic transmission so as to achieve the range selected by the driver.
Examples of conventional position detecting switches of the contact-type are disclosed in Japanese Patent Laid-Open Nos. Hei 8-64077 and 8-64077 wherein movable contacts are pressed against stationary contacts so that electrical conduction is established by contact between the movable and stationary contacts to signal the position of the shift lever.
A conventional contact-type position detecting switch is shown in FIGS. 16 and 17 and has a case body 2, a case cover 3 detachably attached to the case body 2, a rotating shaft 4 that is rotatably supported by the case body 2 and the case cover 3, and a lever-like sliding body 5 mounted for rotation with the rotating shaft 4. The shaft 4 and sliding body 5 rotate in correspondence with movement of a shift lever (not shown) operated by the driver of the automobile.
The case body 2 has a fan shape as shown in FIG. 17. The case body 2 has first and second stationary contacts 6, 7 exposed at both the P and N positions for operating as a contact pair to energize or enable an engine starter circuit, third and fourth stationary contacts 8, 9 at the R position for operating as a contact pair to energize or enable a reverse circuit, a fifth stationary contact 10 exposed at the P, R, 2nd and L positions, a sixth stationary contact 11 exposed at the R, N, D and 2nd positions, a seventh stationary contact 12 exposed at the D, 2nd and L positions, and an eighth stationary contact 13 exposed at the P and 2nd positions. The exposed portions of the stationary contacts 6-13 are shaped and arranged in the case body 2 substantially as concentric arcs about the rotating axis of the rotating shaft 4 disposed in a pivot portion of the fan-shaped case body 2. In this position detecting switch 1, the stationary contacts 10, 11, 12 and 13 in the case body 2 at each of the P, R, N, D, 2nd and L positions are selectively grounded to the case body 2 to generate codes forming position detection signals indicating the selected range position. Thereby the positions for the P, R, N, D, 2nd and L ranges are determined.
The case cover 3 also has a fan shape and defines a fan-shaped space 15 inside the case cover 3. The sliding body 5 is disposed in the space 15 for rotation with the rotating shaft 4.
As shown in FIG. 16, the sliding body 5 has first, second and third cavities or sliding contact receptacle portions 16, 17, 18 that are aligned in a radial direction. First, second and third movable contacts 19, 20, 21 are slidably fitted in the contact receptacle portions 16, 17, 18, respectively, for sliding movement normal to the plane within which the sliding body 5 rotates. The movable contacts 19, 20, 21 are constantly urged from contact receptacle portions 16, 17, 18 into engagement with the case body 2 and the stationary contacts 6-13 by first, second and third coil springs 22, 23, 24, respectively.
When the sliding body 5 is set to the P range position, the first movable contact 19 contacts the first and second stationary contacts 6, 7 and electrically connects the first and second stationary contacts 6, 7, to turn on the starter circuit, thereby establishing a state where the engine is allowed to be started. Simultaneously, the second movable contact 20 contacts the fifth stationary contact 10, and the third movable contact 21 contacts the eighth stationary contact 13, so that the fifth and eighth stationary contacts 10, 13 are electrically connected to the case body 2. Thereby, a position detection signal for the P range of the position circuit is output.
When the sliding body 5 is set to the R range, the first movable contact 19 contacts the third and fourth stationary contacts 8, 9 and electrically connects the third and fourth stationary contacts 8, 9, to turn on the reverse circuit. Simultaneously, the second movable contact 20 contacts the fifth and sixth stationary contacts 10, 11 to electrically connect the fifth and sixth stationary contacts 10, 11 to the case body 2. Thereby, a position detection signal for the R range of the position circuit is output.
When the sliding body 5 is set to the N range position, the first movable contact 19 contacts the first and second stationary contacts 6, 7 and electrically connects the first and second stationary contacts 6, 7, to turn on the starter circuit, thereby allowing the engine to be started, as in the case of the P range. Simultaneously, the second movable contact 20 contacts the sixth stationary contact 11, and the third movable contact 21 contacts the eighth stationary contact 13, so that the sixth and eighth stationary contacts 11, 13 are electrically connected to the case body 2. Thereby, a position detection signal for the N range of the position circuit is output.
When the sliding body 5 is set to the D range, the second movable contact 20 contacts the sixth stationary contact 11, and the third movable contact 21 contacts the seventh stationary contact 12, so that the sixth and seventh stationary contacts 11, 12 are electrically connected to the case body 2. Thereby, a position detection signal of the D range of the position circuit is output.
When the sliding body 5 is set to the 2nd range, the second movable contact 20 contacts the fifth and sixth stationary contact 10, 11, and the third movable contact 21 contacts the seventh and eighth stationary contacts 12, 13, so that the fifth, sixth, seventh and eighth stationary contacts 10, 11, 12, 13 are electrically connected. Thereby, a position detection signal of the 2nd range of the position circuit is output.
When the sliding body 5 is set to the L range, the second movable contact 20 contacts the fifth stationary contact 10, and the third movable contact 21 contacts the seventh stationary contact 12, so that the fifth and seventh stationary contacts 10, 12 are electrically connected to the case body 2. Thereby, a position detection signal of the L range of the position circuit is output.
Thus, the range position of the position detecting switch, that is, the range set by a driver, is detected in accordance with the connection between the movable contacts 19, 20, 21 and the stationary contacts 6, 7, 8, 9, 10, 11, 12, 13.
In the above-described contact-type position detecting switch 1, as shown in FIG. 18, inside opposite end wall surfaces 16a, 16b of the first contact receptacle 16 in the sliding body 5 are inclined with a draft taper angle .alpha., for processing and assembly reasons. The inside opposite end wall surfaces 16a, 16b face in the direction of the length of the sliding body 5 and retain the first movable contact 19 against movement along the length of the sliding body 5. The inside length dimension of the first contact receptacle 16 gradually increases progressing from the innermost wall surface of the first movable contact receptacle portion 16 toward the first and second stationary contacts 6, 7. Although not shown, the second and third movable contact receptacle portions 17, 18 are similarly formed with a draft taper angle .alpha..
However, the foregoing conventional contact-type position detecting switch 1 is designed to be mounted directly on an automatic transmission. Therefore, the position detecting switch 1 is placed in a thermally tough environment where it receives heat from the automatic transmission. Because of the thermal effect of the automatic transmission, the sliding body 5 deforms through thermal expansion and contraction. If the sliding body 5, for example, thermally contracts in a direction indicated by an arrow in FIG. 19, an inside wall surface 16a of the first movable contact receptacle portion 16 may engage one outside wall surface 19a of opposite end wall surfaces 19a, 19b of the movable contact 19 facing lengthwise, at a point .beta. at a height h above the top surfaces of the first and second stationary contacts 6, 7.
When the first contact receptacle wall 16a engages the first movable contact 19, an external force F is applied by the first contact receptacle wall 16a to the end wall 16a of the first movable contact 19 at the point .beta.. Due to friction resistance between the first movable contact 19 and the first and second stationary contacts 6, 7, the external force F causes a rotating moment M in the first movable contact 19, whereby the first movable contact 19 pivots about point .gamma. at a corner portion of the second stationary contact 7 and the bottom contact engaging surface of the contact 19 becomes inclined with respect to the plane of contacts 6 and 7. Thereby, the first movable contact 19 is held in an inclined posture by the first contact receptacle wall 16a contacting the first movable contact 19 as shown in FIG. 19. In this posture, it is likely that the first movable contact 19 will be entirely separated from the first stationary contact 6 and partially disengaged from the second stationary contact 7. Thus the first movable contact 19 fails to achieve reliable contact with the first and second stationary contacts 6, 7 and there is insufficient electric conduction between the contacts 6, 7 and 19.
Furthermore, there may occur an imbalance of load by a first spring 22, as shown in FIG. 20, pressing the first movable contact 19 against the first and second stationary contacts 6, 7. Spring load imbalance can be caused when the acting center of load of the first spring 22 deviates, for example, by an amount a to the right as indicated in FIG. 20. Such a load center deviation also causes a rotating moment M in the first movable contact 19, whereby the first movable contact 19 may well become inclined and fail to achieve reliable contact with the first and second stationary contacts 6, 7 thus failing to achieve sufficient electric conduction between the contacts 6, 7 and 19.
Further, the interval L between the first and second stationary contacts 6, 7 is relatively small as indicated in FIG. 21, the seating of the first movable contact 19 on the first and second stationary contacts 6, 7 may become unstable, increasing the likelihood that the first movable contact 19 will incline. If this happens, reliable contact between the first movable contact 19 and the first and second stationary contacts 6, 7 will fail and, therefore, sufficient electric conduction between the contacts 6, 7 and 19 will not be achieved.
The aforementioned problems with the first movable contact 19 illustrated in FIGS. 19-21 can also occur to the second and third movable contacts 20, 21.